<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/jquery-3.6.0.min.js"></script>
    <style>
        .search {
            width: 170px;
            margin: 100px;
            position: relative;
        }
        
        .con {
            position: absolute;
            top: -40px;
            width: 171px;
            border: 1px solid rgba(0, 0, 0, 0.2);
            box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
            padding: 5px 0;
            font-size: 18px;
            line-height: 20px;
            color: #333;
            display: none;
        }
        
        .con::before {
            content: '';
            width: 0px;
            height: 0px;
            position: absolute;
            top: 28px;
            left: 18px;
            border: 8px solid #000;
            border-style: solid dashed dashed;
            border-color: #fff transparent transparent;
        }
    </style>
</head>

<body>
    <div class="search">
        <div class="con"> </div>
        <input type="text" placeholder="请输入快递单号" class="jd">
    </div>
</body>
<script>
    //JavaScript写的
    // var jd = document.querySelector('.jd')
    // var con = document.querySelector('.con')
    // jd.addEventListener('keyup',function(){
    //     if (this.value == '') {
    //     con.style.display = 'none' 
    //     }else {
    //         con.style.display = 'block'
    //         con.innerHTML = this.value
    //     }
    // })
    // jd.addEventListener('blur',function(){
    //     con.style.display = 'none'
    // })
    // jd.addEventListener('focus',function(){
    //     if (this.value != '') {
    //                 con.style.display = 'block'
    //     }
    // })

    //jQuery写的
    $(document).ready(function () {
    var $jd = $('.jd')
    var $con = $('.con')

    $jd.on('keyup',function(){
        if ($(this).val() == '') {
            $con.hide()
        }else {
            $con.show().html($(this).val())
        }
    })
    $jd.on('blur',function(){
        $con.hide()
    })
    $jd.on('focus',function(){
        if ($(this).val() != '') {
            $con.show()
        }
    })
    })

</script>

</html>